A variety of ceiling- or wall-mounted air distribution devices or diffusers are known that supply ducted air to the room in which they are mounted. These devices generally have an air inlet connecting to the duct system and an air outlet with flow-directing features such as vanes, baffles and/or a perforated face plate. The flow-directing component may be mounted directly to the inlet duct. Alternatively, the air supplied by the inlet duct may be collected in a plenum chamber in the wall or ceiling prior to distribution in the room. The air pressure of the plenum is greater than that of the outside atmosphere.
Conventional "horizontal" air flow diffusers are generally mounted above a ceiling with the face of the flow directing component co-planar with the ceiling. Typically, directional vanes are used to deflect air horizontally through perforations in the face of about 3/16 in. in diameter. This relatively large perforation size permits the supply air to issue from most of these devices in jets with high initial velocity. The air throw, or maximum distance from the outlet at which a specified air velocity can be measured, that is produced is relatively long. The Jets induce the room air and achieve its mixing with the supply air. However, at the large volumes required for high air change rates, these high jet velocities can produce unacceptably high room air velocities.
Laminar flow diffusers that provide "vertical" air flow are also typically mounted in a ceiling with the face coplanar with the ceiling. A deflector in the plenum above the face directs air vertically through perforations in the face that are smaller than those in horizontal air flow diffusers, generally about 1/16 in. in diameter. This smaller aperture size offers significant resistance to the supply air. Consequently, the supply air tends both to fill the plenum more completely than in a device with larger perforations, and to expand more completely across the face of the diffuser as it issues. This results in lower initial face velocity and less entrainment of the room air than would occur with high velocity jets. Thus, in contrast to horizontal diffusers, laminar flow diffusers typically have very low initial velocities, short throws, and low levels of aspiration.
Another type of air diffuser is the "trough" type diffuser, introduced by E.H. Price Limited of Winnipeg, Manitoba in the 1970's, which has a flow directing component that suspends below the ceiling in a triangular prism shape. The flow directing component has vanes to direct air horizontally, and fits directly below the ceiling air duct, with no plenum in between. This device generally has a face with larger perforations, of about 3/16 in. in diameter. The Model GFY high capacity diffuser made by the Barber-Colman Company of Rockford, Ill. uses a similar design for two-way horizontal air distribution.
More recently introduced diffusers create a "radial" or semi-cylindrical flow of air into the room. These are designed to meet the need for high capacity, non-mixing air distribution.
One such device is the Duct-D-fuser.TM. made by United Sheet Metal Division of United McGill Corporation, Columbus, Ohio. This device is essentially the extension of a cylindrical metal air duct into a room. The end of the duct in the room is closed off and the portion of the duct in the room has one of a variety of perforation patterns in its sides. This device is intended primarily for industrial applications.
Another diffuser that can produce a radial flow is the Fusa-Vent.TM. made by Precision Air Products Company of Delano, Minn. This device has a trapezoidal diffuser cage that is installed directly below a ceiling air duct. Adjustable air deflectors are mounted inside the diffuser cage along the two edges where bottom wall meets side walls. The deflectors can be positioned to produce horizontal, vertical or intermediate air patterns. The diffuser may further be adjusted by raising or lowering its orifice cover, which is spring-mounted.
A third type of radial diffuser is described in U.S. Pat. No. 4,616,558 and Canadian Patent No 1,234,312, and sold by Krueger of Tucson, Ariz. and Krueger Air Canada of Weston, Ontario. This device has a box-shaped plenum for installation above the ceiling and a flow directing assembly that suspends below the plane of the ceiling. The bottom wall of the plenum that separates these two components is perforated. The flow directing assembly has a perforated face interior to which are curved directional vanes. Perforation size is of the range of 1/16 to 3/16 in. in diameter. The face is semi-elliptical in cross section with side wall portions that are inclined inwardly from the vertical at the top. The inwardly inclined portions allow air flow to be directed in paths generally parallel to the ceiling, whereas the overall pattern of air flow is radial. The patent specification describes a horizontal, adjustable perforated baffle of approximately the same dimensions as the air duct for placement inside the plenum.
Devices that use circular or curved perforated screens, as these radial diffusers do, have not been generally well accepted in the air distribution industry, primarily due to high tooling costs and limited application to commercial office space.
Certain other air distribution devices are described below to present an overview of the known art.
U.S. Pat. No. 3,084,609 describes a filter diffuser that produces a semi-spherical air distribution pattern, with an inverted dome shape made of multi-ply expanded aluminum sheets or foil. The device is mounted directly below an air duct with no intervening plenum. According to the disclosure, the air passing through the filter is distributed at all angles in the room without the use of baffles or directional vanes. A metal disc is located in the bottom of the dome to prevent air discharge directly downward. In another embodiment, the filter diffuser may have a basket or dishpan shape.
U.S. Pat. No. 3,548,735 describes an air distribution device that is mounted in the ceiling directly below an air duct so that the perforated outlet is coplanar with the ceiling. The device has a plurality of pivotal directional vanes that may be arranged in different patterns for one, two, three, or four-way and vertically downward air distribution.
U.S. Pat. No. 3,559,560 describes a ceiling box for downward air distribution that is installed below an air duct. The bottom of the box is a grille that is substantially flush with the ceiling, through which air is discharged to the room. An end or side wall of the ceiling box is secured to a ceiling joist. The box walls have at their bottom an inwardly projecting flange that supports the grille.
U.S. Pat. No. 4,034,659 describes an array of air diffusion modules, wherein, according to the disclosure, the air flow of each module can be monitored and adjusted to produce a balanced distribution of air from all the modules. This is achieved for each module by a valve controlling the admission of pressurized air into an upper control plenum located above a lower distribution plenum. At the bottom side of each module's lower distribution plenum is a perforated diffusion plate that is contiguous with the ceiling. The diffusion plate is hingedly attached, and may swing down to a vertical position to allow access to the interior. A perforated deflection angle plate with two outwardly and downwardly extending legs exists on the interior of the perforated diffusion plate and swings down with it.
U.S. Pat. No. 4,693,176 describes an air outlet for room conditioning systems to be mounted in a ceiling directly below an air intake duct. This device requires fixed vertical deflectors below the duct that extend downward to the plane of the ceiling. Below the ceiling plane are pivotal slats in the casing portion of the device. Each slat is composed of two vanes that form an obtuse angle, and is pivotal about their junction point. The vanes are unequal in width, with the upstream vane of each slat being shorter in the air flow direction. According to the disclosure, this device has a perforated plate below the air duct and above the fixed deflectors.
U.S. Pat. No. 5,054,379 describes an air release box with a box housing having at least one perforated bottom wall and two perforated side walls, as well as end walls that are not perforated. The side and end walls connect to the cover that carries the connection air inlet. Spin outlet means are arranged in at least the central perforated bottom wall section and in the perforated side wall sections. Two baffle guide plates extend from the bottom walls toward the air inlet. The baffle plates are hingedly attached and angularly adjustable.